The present invention relates generally to method and apparatus for separating particulate or granular material through use of an air stream.
Prior art air separating devices may be functionally grouped into two general categories: classifying devices which separate particulate material of approximately the same density based upon particle size; and sorting devices which separate granular mixtures containing different materials of different densities, e.g. materials such as gold and sand, into constituent components.
Air classifying devices are described in Stebbins, U.S. Pat. No. 1,834,981; Edwards, U.S. Pat. No. 3,948,764; Khag, U.S.S.R. Patent No. 732-033; each of which is hereby specifically incorporated by reference for all that is disclosed therein.
Air sorting devices are described in Stein, U.S. Pat. No. 916,625; Breiholtz et al., U.S. Pat. No. 3,799,339; and applicant's Patent. No. 4,519,896; each of which is hereby specifically incorporated by reference for all that is disclosed therein.
Some prior art devices might be considered combination sorting and classifying devices. One such device is described in Stoner, U.S. Pat. No. 2,210,103. The Stoner device separates material having constituent particles of different size and different density such as raisins and raisin stems.
Air sorting devices rely on weight differences between similarly sized particles for performing the sorting function and thus generally require prescreening of material before it is inserted into a separating airflow, see, e.g., Vickery, U.S. Pat. No. 4,519,896, column 3, lines 29-51, column 4, lines 21-68, and column 5, lines 1-6. In many commercial applications, such as the separation of gold from placer sand, the cost of prescreening the material to be separated is significantly greater than the cost associated with the air separation process. One reason for this substantial cost is that screening equipment is relatively expensive and requires frequent screen replacement and repair. Another reason for the substantial cost associated with screening is that a screening operation requires frequent operator intervention to dislodge near-size particles which become lodged in the screen mesh. Screen "plugging" problems become especially pronounced when the material to be screened contains a wide range of particle diameters. As a result of frequent operation shutdown for maintenance and repair, a screening operation also significantly limits the material through-put in airflow-type gold separating operations. It is one object of the present invention to significantly reduce or eliminate the need for material screening in material separating operations.
Applicant has also developed a number of refinements which improve the operation of a sorting device of the general type described in applicant's U.S. Pat. No. 4,519,896. Thus, it is an object of the present invention to provide a highly effective air sorting device.
Applicant has also discovered that an air separating device such as that described herein is extremely effective as a classifying device. Thus, it is an object of the present invention to provide a highly effective air classifying device.